From a0e37fe35b1af9f607600d2e792e2ff56796af6e Mon Sep 17 00:00:00 2001
From: Chris Loer <chris.loer@gmail.com>
Date: Tue, 6 Jun 2017 09:01:17 -0700
Subject: [core] Hold on to tile yStretch value for rendering old symbolBuckets
 while waiting for new ones.

---
 src/mbgl/tile/geometry_tile.cpp | 11 +++++++++--
 src/mbgl/tile/geometry_tile.hpp |  1 +
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/mbgl/tile/geometry_tile.cpp b/src/mbgl/tile/geometry_tile.cpp
index ad5c2edd4c..1ee303b50f 100644
--- a/src/mbgl/tile/geometry_tile.cpp
+++ b/src/mbgl/tile/geometry_tile.cpp
@@ -42,7 +42,8 @@ GeometryTile::GeometryTile(const OverscaledTileID& id_,
              parameters.pixelRatio),
       glyphManager(parameters.glyphManager),
       imageManager(parameters.imageManager),
-      placementThrottler(Milliseconds(300), [this] { invokePlacement(); }) {
+      placementThrottler(Milliseconds(300), [this] { invokePlacement(); }),
+      lastYStretch(1.0f) {
 }
 
 GeometryTile::~GeometryTile() {
@@ -143,6 +144,9 @@ void GeometryTile::onPlacement(PlacementResult result) {
     if (result.iconAtlasImage) {
         iconAtlasImage = std::move(*result.iconAtlasImage);
     }
+    if (collisionTile.get()) {
+        lastYStretch = collisionTile->yStretch;
+    }
     observer->onTileChanged(*this);
 }
 
@@ -265,7 +269,10 @@ void GeometryTile::querySourceFeatures(
 }
 
 float GeometryTile::yStretch() const {
-    return collisionTile->yStretch;
+    // collisionTile gets reset in onLayout but we don't clear the symbolBuckets
+    // until a new placement result comes along, so keep the yStretch value in
+    // case we need to render them.
+    return lastYStretch;
 }
 
 } // namespace mbgl
diff --git a/src/mbgl/tile/geometry_tile.hpp b/src/mbgl/tile/geometry_tile.hpp
index 3e2efe1093..943296e01b 100644
--- a/src/mbgl/tile/geometry_tile.hpp
+++ b/src/mbgl/tile/geometry_tile.hpp
@@ -122,6 +122,7 @@ private:
     std::unique_ptr<CollisionTile> collisionTile;
     
     util::Throttler placementThrottler;
+    float lastYStretch;
 
 public:
     optional<gl::Texture> glyphAtlasTexture;
-- 
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